1. Field of the Invention
The present invention relates to an information processing apparatus, an image forming apparatus, an image processing method, and a non-transitory computer-readable medium.
2. Description of the Related Art
With regard to inkjet printers, or the like, the conventional technique for converting the printing resolution into a low resolution for printing is generally known as a technique for increasing the speed of printing. If the printing resolution is lower than the resolution of an input image, it is necessary to perform a resolution conversion operation on the input image so as to reduce it into a printable resolution.
One of the above-described resolution conversion methods is the method that is disclosed in Japanese Patent Application Laid-open No. 2014-149260 that is previously filed by the applicant of the subject application. Hereinafter, this method is referred to as the “reference shift” method in this specification.
FIG. 22 is an explanatory diagram of the “reference shift” method.
FIG. 22 illustrates an image G1 before resolution conversion and an image G2 after resolution conversion performed on the image G1 by using “reference shift”.
Each of the images G1 and G2 is illustrated, where the horizontal is in a main scanning direction, the vertical is in a sub-scanning direction, and the image is separated by blocks in units of pixel. Each of the images G1 and G2 is attached with the numbers from a0 to a9 in the main scanning direction and from b0 to b9 in the sub-scanning direction, indicating the pixel position before resolution conversion. The shaded area (also referred to as the colored area) in FIG. 22 indicates a pixel that forms an object, such as a character or a line.
For the “reference shift”, the pixel of interest is set in an image before resolution conversion. Furthermore, reference is made to the pixel values of the pixel of interest and a pixel that follows the pixel of interest and that is located in a direction in which the resolution is decreased and on the downstream side for data processing, and the value, which is obtained by applying a predetermined weight to the pixel values, is set in one corresponding pixel after resolution conversion.
In the example illustrated in FIG. 22, the resolution of the image G1 in the sub-scanning direction is converted by ½. Therefore, with regard to the column of b0, for example, the pixel (a0, b0), which is in the start position for data processing, is first set as the pixel of interest. Next, reference is made to the pixel (a1, b0) that is the pixel that follows the pixel of interest and that is located in the direction (in this case, the sub-scanning direction) to decrease the resolution and on the downstream side for data processing. Furthermore, a predetermined weight is applied to the pixel value of each of the pixel of interest and the reference pixel so that the pixel value of one pixel (a0 to a1, b0) after resolution conversion is obtained. If the pixel of interest and the reference pixel before the resolution conversion is white (the pixel value 0) that does not form an object, such as a character or a line, it is treated as having no pixel value, and the pixel after the resolution conversion is also white. Therefore, the pixel (a0 to a1, b0) is white. In the same manner, as the subsequent two pixels, i.e., the pixel (a2, b0), which is the pixel of interest, and the pixel (a3, b0), which is a reference target, are also white, the pixel after the resolution conversion is white.
As for the pixel (a4, b0), which is the subsequent pixel of interest, and the pixel (a5, b0), which is the reference target, the pixel of interest is white, and the reference target pixel is colored. In this case, the “reference shift” is conducted, i.e., the pixel of interest is shifted to the colored pixel (a5, b0), and the reference target is shifted to the subsequent pixel (a6, b0). Then, a predetermined weight is applied to each pixel value to obtain a pixel value, and it is the pixel value of the pixel (a4 to a5, b0) after the resolution conversion. With regard to the subsequent pixels, the resolution conversion is performed while the state is maintained such that the pixel of interest and the reference pixel are shifted until a pattern with a predetermined condition appears, for example, three white pixels continue. When the pattern with the predetermined condition appears, the shifted state of the pixel of interest and the reference pixel, which are shifted due to the “reference shift”, is reset. The same operation is performed on the columns of b1 to b9.
In some patterns of objects, “jaggy” occurs after resolution conversion is conducted by using the “reference shift” method. “Jaggy” refers to a dot that intermittently appears on an edge portion of a line, character, or the like, when the image after resolution conversion is printed.
FIG. 23 is an explanatory diagram of the mechanism where “jaggy” occurs.
An image G1-1, illustrated in FIG. 23, is an example of the pattern of an object where “jaggy” occurs after resolution conversion is performed by using the “reference shift” method.
An image G2-1 is an image that is obtained by performing resolution conversion on the image G1-1 by using the “reference shift” method. On the image G2-1, the colored pixels in the b4 column to the b6 column are the pixels that are obtained by using the “reference shift” method. On this pattern, a desired result is obtained with regard to all the pixels except for the pixel (a6 to a7, b3) with a mark M1 in the b3 column.
On the image G1-1, during the resolution conversion on the b3 column, in the same manner as the resolution conversion that is explained by using the b1 column as an example, the pixel value of the pixel (a0 to a1, b3) on the image G2-1 is first obtained from the pixel values of the pixel (a0, b3) and the pixel (a1, b3), and then the pixel value of the pixel (a2 to a3, b3) on the image G2-1 is obtained from the pixel values of the pixel (a2, b3) and the pixel (a3, b3).
During the subsequent calculation of the pixel value of the pixel (a4 to a5, b3) on the image G2-1, the pixel of interest and the reference pixel are not shifted so that the pixel (a4, b3) is the pixel of interest and the subsequent pixel (a5, b3) is the reference target. Both of these pixels are colored pixels. If a predetermined weight is applied to the pixel values to obtain a pixel value, the pixel value of the pixel (a4 to a5, b3) on the image G2-1 is colored (dark color in this example).
During the subsequent calculation of the pixel value of the pixel (a6 to a7, b3) on the image G2-1, as the pixel (a6, b3), which is the pixel of interest, is colored, the “reference shift” is not conducted, and the subsequent pixel (a7, b3) is the reference target. If a predetermined weight is applied together with the white pixel (a7, b3), which is the reference target, so that a pixel value is obtained, the pixel value of the pixel (a6 to a7, b3) on the image G2-1 is colored (light color in this example).
Conversely, with regard to the b4 column to the b6 column, the “reference shift” is conducted on the a4 row. Therefore, each of the pixels in the a5 row and the a6 row is included in the next upper pixel after the resolution conversion. As a result, the colored pixel (a6 to a7, b3) intermittently remains on the edge portion of the object, as indicated by the mark M1 on the image G2-1. If this image is printed, a dot intermittently appears on the edge portion of the object.
This phenomenon occurs in the position where the number of pixels is changed, or the like, if the number of pixels that form an object is not uniform in the direction to decrease the resolution. As the effect of maintaining the image quality due to the resolution conversion by using the “reference shift” method is high, there is a demand for an improvement for “jaggy”.
Therefore, it is desirable to provide an information processing apparatus, an image forming apparatus, an image processing method, and a non-transitory computer-readable medium capable of reducing “jaggy” of an image after resolution conversion by using the “reference shift” method.